I'm trying to give my merc and my zealot gears with integral DR to deal with the tomb vipers, but I'm not sure how much DR is enough. From the Arreat Summit there're 2 melee attacks by the vipers. Is the poison cloud damage listed as melee attack 2 (i.e. 51-89)?

On gear selection, I can only think of Gladiator's Bane and Gerke's Sanctuary. Any good helm?

The problem with vipers is that the poison cloud damage is bugged. I can't remember the exact details, but from my last nil run, the cloud continues to hit repeatedly while moving in cloud - which is what tends to kill the merc, and you if not careful.

Shanksie: I'm particularly interested in your build. Sol's in IK helm and armor means 21 DR. Is that all you need? Or am I mistaken that you just howl the vipers away and they won't attack you?

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Yeah it's just the standard IK WW build so decent amounts of life, just the 3 sols (dual shael in maul ofc).

It's a combination of both i think, in that i do howl some of them away and I can leap over some of the packs aswell. The ones that do attack me don't cause me too much problems, tho ofc on a Barb i have a good BO so lots of life to play with.

What follows is a detailed explanation of Tomb Viper cloud mechanics: if you just want to know their physical damage per collision, scroll to the bottom.

The Tomb Viper's A1 attack has a missile assigned to it (viper_poisjav in Missiles.txt) and this attack applies both physical and poison damage, 100% of which is applied by this javelin on collision. Since the javelin is destroyed on impact, this damage is only applied once.

However, this javelin can release up to 14 clouds in its wake (viper_poisjavcloud in Missiles.txt), each of which applies 100% of the javelin's damage. This means that they apply the A1 attack's physical and poison damage on collision too: although these clouds aren't destroyed on impact and they linger, Last Collide is enabled, which normally prevents a missile from colliding with its last target and thus applying its damage or effects again.

There are two circumstances in which the physical and poison damage of the clouds can be applied multiple times in quick succession. The first is when you move and collide with multiple clouds: since Tomb Vipers spawn in groups of 2-3, a single salvo of 2-3 javelins can generate up to 28-42 clouds and moving through them can thus result in damage being applied up to 28-42 times. The second is when two targets are overlapping or standing close enough together to collide with the same cloud(s): since enabling Last Collide only prevents a missile from colliding with its last target, each cloud collides with the targets alternately and thus applies its damage every other frame (averaging 12.5 times per second).

Obviously players have complained about this, but unfortunately these complaints met with the following post on the Battle.net forums:

MicahW said:

Working as intended.

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Based on what's already been described, that's probably true from a coding perspective: apart from everything else, viper_poisjavcloud is the only missile which uses the SrcMissDam column in Missiles.txt (this is what makes it apply the javelin's damage), suggesting this column may have been inserted for this specific case. Last Collide probably works as intended, since otherwise information would have to be stored of every single target hit by every single missile for which it was enabled.

However, there is one way in which the clouds are almost certainly bugged (or at least not working as intended, unless Blizzard are evil): they're only supposed to last for 2.4 seconds (60 frames). While they do so visibly, they last for at least another 4.8 seconds (120 frames) invisibly.

To avoid multiple collisions and thus multiple applications of damage a player should stand still, away from any other targets and not move for at least five seconds after the clouds have apparently disappeared. Note that Teleporting with a hireling or pet won't necessarily keep you safe: if a Sorceress teleports into a cloud with a hireling, the cloud will still collide alternately with both of them... and if she teleports into multiple clouds...

Another possibility is negating the damage so that it doesn't matter how many collisions there are. Since poison damage is designed to be applied every frame, the damage which is applied by each collision is negligible: at worst, when a cloud's Last Collide is overridden extra frames of poison damage will be applied every other frame, increasing the rate of damage by 50% and resetting the length for which that rate is applied. Furthermore, when Last Collide is overridden each additional cloud should increase the rate of damage by 50%: two clouds will double the rate (+100%), four clouds will triple it (+200%), and so on.

The danger comes from multiple applications of the modest physical damage, which increases by 6.25% with every additional player in Ladder and single-player games in Nightmare and Hell, can be increased by +% Enhanced Damage and doubled by a critical hit (although these only occur on 5% of collisions). On the flip side, cloud collisions can be blocked and an Assassin's Weapon Block and an Amazon's Avoid and Evade are effective.

No random Champion or Unique Tomb Vipers spawn in the Halls of Vaught, so the only ones you'll find are those that spawn from Evil Urns or in set locations at the end of the halls: if you know how to find Nihlathak, then you never need to encounter them (and it's certainly worth avoiding Champions, or Extra Strong Tomb Vipers that spawn Aura Enchanted and Cursed... and damage of other types can also be added by elemental enchantments). However, Nihlathak himself can be enchanted with Might (level 12 applying +150% ED in Nightmare, level 15 applying +180% ED in Hell) or Fanaticism (level 9 applying +93% ED in Nightmare, level 11 applying +110% ED in Hell). Below is the physical damage the javelin and clouds will apply under various conditions, rounded up to the nearest point when +% ED is applied:

Since integer damage reduction is applied before percentage damage reduction (also known as Damage Resist %), if you're cursed with Amplify Damage (DR -100%) this isn't really an issue when no +% ED is applied if you're equipping DR >43 in an eight-player game (although the occasional critical hit will hurt more unless you're equipping DR >87).

The bright side of +% ED applying to cloud damage is that -% ED also does so: casting Weaken (-33% ED), Decrepify (-50% ED), Battle Cry (-(24+(1*lvl))% ED) or Taunt (-(3+(2*lvl))% ED) will decrease physical damage, although the impact will be much less significant when +% ED is also being applied.

I am not a player who runs areas, so I meet them at most once per difficulty and character. This means I can take my time with them to avoid danger. IÂ´ve found out that the missiles are not that hurtful if you donÂ´t move towards the viper. Standing still or moving only sideways seem to help a lot.